A magnetic recording tape is usually composed of a polyester support having provided thereon a magnetic recording layer which contains magnetic particles, a binder and various additives. Such a magnetic recording tape has high surface electric resistance because of the high electric resistance of the magnetic particles used and because of electrically insulating materials which are generally employed for preparing the tape, and is easily electrostatically charged by abrasion. The electrostatic charge attracts dust to the surface of the magnetic recording tape, leading to an undesirable increase in the coefficient of static friction, to deformation of the wound shape of the magnetic recording tape and to decreased running properties.
It has been proposed to decrease the surface electric resistance of magnetic recording tapes by incorporating electroconductive substances such as carbon black or an anionic, cationic, nonionic or ampholytic surface active agent into the magnetic recording layer. However, the addition of electroconductive substances in an excess amount results in decreased magnetic flux density and decreases the sensitivity of the magnetic recording medium, and the addition of a surface active agent in an excess amount reduces running properties and makes the medium sticky.
To solve this problem it has been proposed to provide an intermediate layer between the support and the magnetic recording layer and to incorporate into the intermediate layer carbon black, as disclosed in Japanese Patent Application (OPI) No. 55433/80 (the term "OPI", as used herein, refers to a "published, unexamined Japanese Patent Application") and U.S. Pat. No. 3,440,091, and a quarternary ammonium salt which is disclosed in Japanese Patent Application (OPI) No. 60536/82. However, carbon black has a poor dispersibility because of its fine particle size, and its addition decreases the surface smoothness of the intermediate layer. Because of the poor surface smoothness of the intermediate layer, the magnetic recording layer provided thereon also has poor surface smoothness. This poor surface smoothness is a very serious problem in short wavelength recording systems such as VHS or Beta video tape systems, where it causes a decreased video S/N ratio and poor image quality.
If a quarternary ammonium salt is included in an intermediate layer, less of the quarternary ammonium salt exudes to the surface of the magnetic recording layer than if the quarternary ammonium salt is included in the magnetic recording layer. However, this type of surface active agent inherently migrates in the layer, and moves from the intermediate layer through the magnetic recording layer to finally reach the surface of the magnetic recording layer. This leads to decreased video S/N and adversely affects the efficiency of the magnetic recording medium.